In known processes for the shape removal machining of workpieces as are used, for example, in milling processes in machine tool and shaping, the workpiece, which is to be machined to a desired contour in the fabrication processes, is machined with a milling head of a milling machine in a shape-removal procedure. Processes are known in which the reactive movement between the relating mill head and the workpiece to be machined is possible along three linear axes. These three linear axes are typically at angles of 90° to one another and define an orthogonal three-axis coordinate system.
For the machining of more complicated workpiece shapes, especially shapes with deep cavities and/or with undercuts, such three-axis strategies in which the rotating tool is maintained systematically perpendicular to a planar main machining plane are, however, often not sufficient. This, in not the least problem, can permit collisions in regions of steeper geometry of the workpiece between the workpiece and the rotating tool, or its tool holder, or other machine elements.
To avoid such collisions or to enable improvement in the cutting conditions, three-axis relative movements between the tool and the workpiece often are not longer sufficient. For these cases, machining processes are known in which, by providing additional pivotal movements of the workpiece and/or the tool about one or more pivot axes, the machining can be improved. The provision of the two additional pivotal axes of the machine enables the tool to assume orientations which are not orthogonal to the axes of the cartesian machine coordinate system. Depending upon the number of these additional rotary or pivotal axes, one may have reference to 4-axis or 5-axis machining or, alternately, also to 3+1 axes or 3+2 axes machining. In these cases, a machine-specific formulation of a (NC) or Numerical Control program is required. Independently from the kinematics of the machine, the inclined orientation of the tool to the workpiece can also be described by a unit vector of the tool orientation which enables programming in a machine-independent mode. For this purpose in the program of the angle of the unit feature, or the axis for the tool orientation, the programming requires explicitly defining each point for the machining operation.
To establish a collision-free 5-axis machining program, initially a calculation is made without an inclined positioning of the rotatable tool, after which, to avoid collisions between the tool and the workpiece, the angle required is integrated subsequently in the program for the requisite position of the tool. The tool setting required for the collision-free machining can either be estimated for the critical regions which may occur, determined by CAD programs, or established by so-called “teaching” in testing of the machining program on the machine. Advantageously, in this method, a relatively simple arrangement of adjoining machining regions is provided so that the controls of the machining paths can be controlled relatively well. Nevertheless, the system requires comparatively high costs to ensure collision-free machining since the movement paths of the tool and workpiece holder must either be tested on a point-by-point basis, or must be simulated using additional simulation software, or both.
In a further machining method for segmentwise fixed tool settings, the machining operation is calculated with a corresponding tilted coordinate system which can result in a tested collision-free operation over an entire machining region. However, for this method a secondary higher cost must be taken into consideration because of the need for more complex machining segments with the collision-free settings that frequently can only be determined by iterative processes. As a consequence, the overall controlling of the pattern of the machining paths is more difficult.
An alternative to the described methods is the creation of so-called 5-axis simultaneous programs, that is, machining programs in which simultaneous movements of the machine tool, both along the linear axis and also the pivotal axis, are created. In this case, the setting of the rotating tool can be varied permanently with its advance along its machining path.
The problems in this process lie less in the theoretical concepts than in the limitations of the machine tool which is generally used because their mechanical, or control, and regulation technology characteristics frequently do not afford the requisite machining processions or supply the desired machining qualities. Thus, with simultaneous 5-axis machining by presently available machining technology, there are very narrow limitations. The kinetic configuration of the machine tools typically require heavy machine tools and frequently large spacings between the pivot axes and the workpieces so that, even in the construction of the tool, the smallest imperfections in the movement patterns of the rotating tool can have a significant negative effect on the processes of the machining results. The inertia of the moving masses of the pivotal toolhead also can have a negative effect on the dimensional stability in the machining of the workpiece. Thus, for example, control errors in the segment of minutes of a degree can lead to deviations in the workpiece contour of several tenths of a mm. In machine tool operations, typical precisions only in the range of 0.005 mm to up to 0.03 mm may be tolerable. As a result, the suitability of such machines for 5-axis simultaneous machining is greatly limited.